Hi Clement,
Good idea!
Actually I believe that SPCA have their own donation boxes that are placed at certain locations. I am not sure if they would directly authorize someone to place their own SPCA donations box though, for fear of some people defrauding the public.
Since your customer is in Penang, I suggest that he check with SPCA Penang if they have such an arrangement, or if SPCA Penang can authorize him to do so on a personal basis. It would definitely be great if he can help collect some funds for them. If you have customers in Klang valley willing to do so as well, I will check with SPCA Selangor and PAWS to see what arrangements they can work out.